Making metal foundry sand molds



Patented July 5, 1938 rmxnie nr'rnr FOUNDRY SAND MoLns Victor Stobie, Harrogate, England Application January. 18, 1937, Serial No. 121,208 In Great Britain November 21, 1935.

2 Glaims.

lo mo'lding'boxes by two principal means. One has been to supply compressed. air to the surface of sand in a closed sand container, and to clamp or fasten the molding box to the bottom of the sand container, which latter is provided with an exit through which the sand travels immediately from the sand container into' the molding box. By that method, the molding box forms a closed, or almost closed, receptacle continuous with the machine, and when the sand and its contained compressed air enter the molding box, the air pressure in the molding box rises and becomes a back-pressure acting against the entering sand. Small openings are sometimes provided in the molding box, but they are quickly sealed by the incoming sand and, in any case, the very rapid flow of sand and its contained air into the molding box causes atonce a strong back-pressure of air. This back-pressure becomes greatest in deep recesses inside the molding box, and pre vents the sand being well compacted in those parts of the mold. The sand velocity reduces progressively with the filling of the molding box because the back-pressure increases, so there is absence of uniformity. A further disadvantage of that system is that, as the point of exit of the sand from the sand container is fixed in position relative to the inlet of the molding box clamped to it, most of the sand has to change its direction of travel within the molding box several times before it can fill it. This also acts against the compactness of the sand shape, and the sand may not fill the molding box.

The other principal previous pneumatic sys.

tem of filling molding boxes with bonded sand consists in blowing air from a jet at the end of a pipe into a larger pipe whose opening at one end is axially concentric with the jet, and supplying sand between the jet and the larger pipe so that air from the jet will carry the sand forward into the larger pipe, from the other end of which it flows into the molding box. The disadvantage of this system is that a much larger volume of air is required for a given amount of sand than by the other previous system. The inconveniences of this greater amount of air are: the cost of. theextra compressedair; and the blowing away of sand from the mold" by the high volume of air which accompanies the sand on its exit fromthe pipe into the. mold; ing box. i

By the present invention compressed air is supplied into a closed sand container containing molding sand, and the sand is liberated through an aperture into free atmosphere. The steep pressure gradient thus ruling causes the sand to travel to and through the exit at a much higher velocity than by the described previous system which utilizes a closed sand container. The high momentum gained by the sand at the exit is then utilized to project thesand first across open atmosphere, to liberate the air contained between the grains of the sand, and then into the molding box, where the balance of kinetic energy in the sand expends itself on compacting the sand therein.

In order that the sand may be directly projected into all parts of the molding box, the latter may be moved into difierent positions under the outflowing column of sand. Alternatively, a fixed or flexible pipe may be attached to the sand exit of the sand container, and the sand projected from the other end of that pipe through free atmosphere into the molding box.

In the accompanying drawing, the figure illustrates diagrammatically in elevation, partly sectional, a pneumatically energized sand shape making machine which conforms to one embodiment of the present invention.

Referring to the drawing, there is provided a container l for the sand 2. Overlying the sand is the plunger 3 provided with holes 4, the plunger being free to reciprocate and follow along after the sand as the level of the sand drops with use. The container l is provided with an inlet 5 for compressed air from any suitable source and an outlet 6 for the sand. At the bottom of the container l is a fixed extension 1 which is provided with. a conduit 8 connected with the sand outlet 6. In the modification disclosed. a flexible hose or extension 9 is connected to the conduit 8 by a suitable coupling l0. Adjacent the ultimate sand outlet is themolding box ll into which the sand is to be projected consecutively at difi'erent places or angles, 12 representing the spray of sand projected through free atmosphere into the molding box.

My method of projecting sand through free atmosphere into the molding box is not to be compared with sand blasting systems, nor the air 5s jet method previously proposed for filling molding boxes. The forward movement of the sand by my method is due to the progressive expansion of the compressed air residing between the grains of the sand, whereas all injector or ejector systems operate by the sand being carried, as a passenger, on a moving stream of air from a jet. The sand and the compressed air between its grains do not occupy within the present apparatus a greater volume than does sand alone in open atmosphere. In ejector or injector systems, the injected air is added to the volume of the sand and its already contained air; which is one reason why injector or ejector methods applied to sand molding produce a high ratio of air to sand. Another reason is that sand deflects much of the air stream from the jet into directions not useful for the forward movement of the sand, and therefore more air is necessary to move the sand forward, and much of the wasted air is also carried forward by the stream. Additionally, injectors and ejectors, other than those used with steam condensation for filling boilers with water, are known to be inefiicient unless the aspiration of the material to be moved is effected in a cascaded succession of jets, on the principle of such well known injectors as the Kortin-g and the Eynon-Evans. Such a principle is, however, inoperable with sand, and the inefiiciency of the ordinary type of injector or ejector entails very much of the energy in the compressed air being delivered to the jet being lost and, therefore, large excess of compressed air must be delivered to move the sand forward.

I claim:

1. The method of projecting bonded sand into a molding box consisting in subjecting sand in a closed sand container to air pressure so as to fill the normal spaces between the sand grains with compressed air, letting the sand travel on a steep pressure gradient through an exit from the sand container, through which exit the sand is forced forward by the progressive expansion of the compressed air contained between the sand grains, and passing the sand stream from the end of the exit through open atmosphere into the molding box.

2. The method of making sand shapes in molding boxes comprising subjecting bonded said to air pressure so as to fill the normal spaces between the sand grains with compressed air, forcing the sand forward on a steep pressure gradient by the progressive expansion of the compressed air contained between the sand grains through an exit and passing the sand stream from the end of the exit through open atmosphere into the molding box.

VICTOR STOBIE. 

